This invention is in the field of maize breeding, specifically relating to an inbred maize line designated NP2171.
The goal of plant breeding is to combine in a single variety or hybrid various desirable traits. For field crops, these traits may include resistance to diseases and insects, tolerance to heat and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination and stand establishment, growth rate, maturity, and plant and ear height, is important.
Field crops are bred through techniques that take advantage of the plant""s method of pollination. A plant is self-pollinated if pollen from one flower is transferred to the same or another flower of the same plant. A plant is cross-pollinated if the pollen comes from a flower on a different plant. Plants that have been self-pollinated and selected for type for many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny. A cross between two different homozygous lines produces a uniform population of hybrid plants that may be heterozygous for many gene loci. A cross of two plants each heterozygous at a number of gene loci will produce a population of hybrid plants that differ genetically and will not be uniform.
Maize (Zea mays L.), often referred to as corn in the United States, can be bred by both self-pollination and cross-pollination techniques. Maize has separate male and female flowers on the same plant, located on the tassel and the ear, respectively. Natural pollination occurs in maize when wind blows pollen from the tassels to the silks that protrude from the tops of the ears.
A reliable method of controlling male fertility in plants offers the opportunity for improved plant breeding. This is especially true for development of maize hybrids, which relies upon some sort of male sterility system. There are several options for controlling male fertility available to breeders, such as: manual or mechanical emasculation (or detasseling), cytoplasmic male sterility, genetic male sterility, gametocides and the like.
Hybrid maize seed is typically produced by a male sterility system incorporating manual or mechanical detasseling. Alternate strips of two maize inbreds are planted in a field, and the pollen-bearing tassels are removed from one of the inbreds (female). Providing that there is sufficient isolation from sources of foreign maize pollen, the ears of the detasseled inbred will be fertilized only from the other inbred (male) and the resulting seed is therefore hybrid and will form hybrid plants.
The laborious, and occasionally unreliable, detasseling process can be avoided by using cytoplasmic male-sterile (CMS) inbreds. Plants of a CMS inbred are male sterile as a result of factors resulting from the cytoplasmic, as opposed to the nuclear, genome. Thus, this characteristic is inherited exclusively through the female parent in maize plants, since only the female provides cytoplasm to the fertilized seed. CMS plants are fertilized with pollen from another inbred that is not male-sterile. Pollen from the second inbred may or may not contribute genes that make the hybrid plants male-fertile. Seed from detasseled fertile maize and CMS produced seed of the same hybrid can be blended to insure that adequate pollen loads are available for fertilization when the hybrid plants are grown.
There are several methods of conferring genetic male sterility available, such as multiple mutant genes at separate locations within the genome that confer male sterility, as disclosed in U.S. Pat. Nos. 4,654,465 and 4,727,219 and chromosomal translocations as described in U.S. Pat. Nos. 3,861,709 and 3,710,511, the disclosures of which are specifically incorporated herein by reference. There are many other methods of conferring genetic male sterility in the art, each with its own benefits and drawbacks. These methods use a variety of approaches such as delivering into the plant a gene encoding a cytotoxic substance associated with a male tissue specific promoter or an antisense system in which a gene critical to fertility is identified and an antisense to that gene is inserted in the plant (EPO 89/3010153.8 and WO 90/08828).
Another system useful in controlling male sterility makes use of gametocides. Gametocides are not a genetic system, but rather a topical application of chemicals. These chemicals affect cells that are critical to male fertility. The application of these chemicals affects fertility in the plants only for the growing season in which the gametocide is applied (see Carlson, Glenn R., U.S. Pat. No. 4,936,904, which is incorporated herein by reference). Application of the gametocide, timing of the application and genotype specificity often limit the usefulness of the approach.
The use of male sterile inbreds is but one factor in the production of maize hybrids. The development of maize hybrids requires, in general, the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine the genetic backgrounds from two or more inbred lines or various other germplasm sources into breeding pools from which new inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which of those have commercial potential. Plant breeding and hybrid development are expensive and time-consuming processes.
Pedigree breeding starts with the crossing of two genotypes, each of which may have one or more desirable characteristics that is lacking in the other or which complements the other. If the two original parents do not provide all the desired characteristics, other sources can be included in the breeding population. In the pedigree method, superior plants are selfed and selected in successive generations. In the succeeding generations the heterozygous condition gives way to homogeneous lines as a result of self-pollination and selection. Typically in the pedigree method of breeding five or more generations of selfing and selection is practiced: F1 to F2; F3 to F4; F4 to F5, etc.
A single cross maize hybrid results from the cross of two inbred lines, each of which has a genotype that complements the genotype of the other. The hybrid progeny of the first generation is designated F1. In the development of commercial hybrids only the F1 hybrid plants are sought. Preferred F1 hybrids are more vigorous than their inbred parents. This hybrid vigor, or heterosis, can be manifested in many polygenic traits, including increased vegetative growth and increased yield.
The development of a maize hybrid involves three steps: (1) the selection of plants from various germplasm pools for initial breeding crosses; (2) the selfing of the selected plants from the breeding crosses for several generations to produce a series of inbred lines, which, although different from each other, breed true and are highly uniform; and (3) crossing the selected inbred lines with different inbred lines to produce the hybrid progeny (F1). During the inbreeding process in maize, the vigor of the lines decreases. Vigor is restored when two different inbred lines are crossed to produce the hybrid progeny (F1). An important consequence of the homozygosity and homogeneity of the inbred lines is that the hybrid between a defined pair of inbreds will always be the same. Once the inbreds that give a superior hybrid have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parents is maintained.
A single cross hybrid is produced when two inbred lines are crossed to produce the F1 progeny. A double cross hybrid is produced from four inbred lines crossed in pairs (Axc3x97B and Cxc3x97D) and then the two F1 hybrids are crossed again (Axc3x97B)xc3x97(Cxc3x97D). Much of the hybrid vigor exhibited by F1 hybrids is lost in the next generation (F2). Consequently, seed from hybrids is not used for planting stock.
Hybrid seed production requires elimination or inactivation of pollen produced by the female parent. Incomplete removal or inactivation of the pollen provides the potential for self-pollination. This inadvertently self-pollinated seed may be unintentionally harvested and packaged with hybrid seed. Once the seed is planted, it is possible to identify and select these self-pollinated plants. These self-pollinated plants will be genetically equivalent to the female inbred line used to produce the hybrid. Typically these self-pollinated plants can be identified and selected due to their decreased vigor. Female selfs are identified by their less vigorous appearance for vegetative and/or reproductive characteristics, including shorter plant height, small ear size, ear and kernel shape, cob color, or other characteristics.
Identification of these self-pollinated lines can also be accomplished through molecular marker analyses. See, xe2x80x9cThe Identification of Female Selfs in Hybrid Maize: A Comparison Using Electrophoresis and Morphologyxe2x80x9d, Smith, J. S. C. and Wych, R. D., Seed Science and Technology 14, pp. 1-8 (1995), the disclosure of which is expressly incorporated herein by reference. Through these technologies, the homozygosity of the self-pollinated line can be verified by analyzing allelic composition at various loci along the genome. Those methods allow for rapid identification of the invention disclosed herein. See also, xe2x80x9cIdentification of Atypical Plants in Hybrid Maize Seed by Postcontrol and Electrophoresisxe2x80x9d Sarca, V. et al., Probleme de Genetica Teoritca si Aplicata Vol. 20 (1) p. 29-42.
As is readily apparent to one skilled in the art, the foregoing are only two of the various ways by which the inbred can be obtained by those looking to use the germplasm. Other means are available, and the above examples are illustrative only.
Maize is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop high-yielding maize hybrids that are agronomically sound based on stable inbred lines. The reasons for this goal are obvious: to maximize the amount of grain produced with the inputs used and minimize susceptibility of the crop to pests and environmental stresses. To accomplish this goal, the maize breeder must select and develop superior inbred parental lines for producing hybrids. This requires identification and selection of genetically unique individuals that occur in a segregating population. The segregating population is the result of a combination of crossover events plus the independent assortment of specific combinations of alleles at many gene loci that results in specific genotypes. The probability of selecting any one individual with a specific genotype from a breeding cross is infinitesimal due to the large number of segregating genes and the unlimited recombinations of these genes, some of which may be closely linked. However, the genetic variation among individual progeny of a breeding cross allows for the identification of rare and valuable new genotypes. These new genotypes are neither predictable nor incremental in value, but rather the result of manifested genetic variation combined with selection methods, environments and the actions of the breeder. Thus, even if the entire genotypes of the parents of the breeding cross were characterized and a desired genotype known, only a few, if any, individuals having the desired genotype may be found in a large segregating F2 population. Typically, however, neither the genotypes of the breeding cross parents nor the desired genotype to be selected is known in any detail. In addition, it is not known how the desired genotype would react with the environment. This genotype by environment interaction is an important, yet unpredictable, factor in plant breeding. A breeder of ordinary skill in the art cannot predict the genotype, how that genotype will interact with various climatic conditions or the resulting phenotypes of the developing lines, except perhaps in a very broad and general fashion. A breeder of ordinary skill in the art would also be unable to recreate the same line twice from the very same original parents, as the breeder is unable to direct how the genomes combine or how they will interact with the environmental conditions. This unpredictability results in the expenditure of large amounts of research resources in the development of a superior new maize inbred line.
According to the invention, there is provided a novel inbred maize line, designated NP2171. This invention thus relates to the seeds of inbred maize line NP2171, to the plants of inbred maize line NP2171, and to methods for producing a maize plant by crossing the inbred line NP2171 with itself or another maize line. This invention further relates to hybrid maize seeds and plants produced by crossing the inbred line NP2171 with another maize line.
The invention is also directed to inbred maize line NP2171 into which one or more specific, single gene traits, for example transgenes, have been introgressed from another maize line. Preferably, the resulting line has essentially all of the morphological and physiological characteristics of inbred maize line of NP2171, in addition to the one or more specific, single gene traits introgressed into the inbred, preferably the resulting line has all of the morphological and physiological characteristics of inbred maize line of NP2171, in addition to the one or more specific, single gene traits introgressed into the inbred. The invention also relates to seeds of an inbred maize line NP2171 into which one or more specific, single gene traits have been introgressed and to plants of an inbred maize line NP2171 into which one or more specific, single gene traits have been introgressed. The invention further relates to methods for producing a maize plant by crossing plants of an inbred maize line NP2171 into which one or more specific, single gene traits have been introgressed with themselves or with another maize line. The invention also further relates to hybrid maize seeds and plants produced by crossing plants of an inbred maize line NP2171 into which one or more specific, single gene traits have been introgressed with another maize line. The invention is also directed to a method of producing inbreds comprising planting a collection of hybrid seed, growing plants from the collection, identifying inbreds among the hybrid plants, selecting the inbred plants and controlling their pollination to preserve their homozygosity.
In the description and examples that follow, a number of terms are used herein. In order to provide a clear and consistent understanding of the specification and claims, including the scope to be given such terms, the following definitions are provided. Below are the descriptors used in the data tables included herein. All linear measurements are in centimeters unless otherwise noted.
Heat units (Max Temp( less than =86 deg. F.)+Min Temp( greater than =50 deg. F.))/2-50
EMRGN Final number of plants per plot
KRTP Kernel type: 1. sweet 2. dent 3. flint 4. flour 5. pop 6. ornamental 7. pipecorn 8. other
ERTLP % Root lodging (before anthesis)
GRNSP % Brittle snapping (before anthesis)
TBANN Tassel branch angle of 2nd primary lateral branch (at anthesis)
LSPUR Leaf sheath pubescence of second leaf above the ear (at anthesis) 1-9 (1=none)
ANGBN Angle between stalk and 2nd leaf above the ear (at anthesis)
CR2L Color of 2nd leaf above the ear (at anthesis)
GLCR Glume Color
GLCB Glume color bars perpendicular to their veins (glume bands): 1. absent 2. present
ANTC Anther color
PLQUR Pollen Shed: 0-9 (0=male sterile)
HU1PN Heat units to 10% pollen shed
HUPSN Heat units to 50% pollen shed
SLKC Silk color
HU5SN Heat units to 50% silk
SLK5N Days to 50% silk in adapted zone
HU9PN Heat units to 90% pollen shed
HUPLN Heat units from 10% to 90% pollen shed
DA19 Days from 10% to 90% pollen shed
LAERN Number of leaves above the top ear node
MLWVR Leaf marginal waves: 1-9 (1=none)
LFLCR Leaf longitudinal creases: 1-9 (1=none)
ERLLN Length of ear leaf at the top ear node
ERLWN Width of ear leaf at the top ear node at the widest point
PLHCN Plant height to tassel tip
ERHCN Plant height to the top ear node
LTEIN Length of the internode between the ear node and the node above
LTASN Length of the tassel from top leaf collar to tassel tip
LTBRN Number of lateral tassel branches that originate from the central spike
EARPN Number of ears per stalk
APBRR Anthocyanin pigment of brace roots: 1.absent 2.faint 3.moderate 4.dark
TILLN Number of tillers per plant
HSKC Husk color 25 days after 50% silk (fresh)
HSKD Husk color 65 days after 50% silk (dry)
HSKTR Husk tightness 65 days after 50% silk: 1-9 (1=loose)
HSKCR Husk extension: 1. short (ear exposed) 2. medium (8 cm) 3. long (8-10 cm) 4. very long ( greater than 10 cm)
HEPSR Position of ear 65 days after 50% silk: 1.upright 2.horizontal 3.pendent
STGRP % Staygreen at maturity
DPOPN % dropped ears 65 days after anthesis
LRTRN % root lodging 65 days after anthesis
HU25 Heat units to 25% grain moisture
HUSG Heat units from 50% silk to 25% grain moisture in adapted zone
DSGM Days from 50% silk to 25% grain moisture in adapted zone
SHLNN Shank length
ERLNN Ear length
ERDIN Diameter of the ear at the midpoint
EWGTN Weight of a husked ear (grams)
KRRWR Kernel rows: 1.indistinct 2.distinct
KRNAR Kernel row alignment: 1. straight 2. slightly curved 3. curved
ETAPR Ear taper: 1. slight 2. average 3. extreme
KRRWN Number of kernel rows
COBC Cob color
COBDN Diameter of the cob at the midpoint
KRTP Endosperm type: 1. sweet 2. extra sweet 3. normal 4. high amylose 5. waxy 6. high protein 7. high lysine 8. super sweet 9. high oil 10. other
KRCL Hard endosperm color
ALEC Aleurone color
ALCP Aleurone color pattern: 1. homozygous 2. segregating
KRLNN Kernel length (mm)
KRWDN Kernel width (mm)
KRDPN Kernel thickness (mm)
K100N 100 kernel weight (grams)
KRPRN % round kernels on 13/64 slotted screen
GRLSR Grey leaf spot severity rating; 1=resistent, 9=susceptible.
INTLR Intactness rating of plants at time of harvest; 1=all foliage intact, 9=all plants broken below the ear.
LRTLP Percentage of plants lodged, leaning  greater than 30 degrees from vertical, but unbroken at harvest.
MST_P Percent grain moisture at harvest.
SCLBR Southern corn leaf blight severity rating; 1=resistent, 9=susceptible.
STKLP Percentage of plants with stalks broken below the ear at time of harvest.
YBUAN Grain yield expressed as bushels per acre adjusted to 15.5% grain moisture.
STBWR Stewart Bacterial Wilt
ERLNN Ear Length
CRSTR Common Rust Rating
GRQUR Grain Quality
PLTAR Plant Appearance
HUBLN Heat Units to Black Layer
TSTWN Test Weight in LBS/BU
PSTSP Push Test for Stalk/Root Quality on Erect Plants
ERGRR Early Growth: 6+Leaf Stage